Dry Sanding Surfaces Having High Abrasive Loading

ABSTRACT

Abrasive articles are disclosed that may be used in dry sanding applications. The abrasive articles disclosed may be made entirely from abrasive materials or alternatively may be made by fastening abrasive surfaces to handles or tools. The abrasive articles of the present invention have abrasive surfaces with controlled wear rates that renew themselves during use. The self renewing abrasive surfaces of the present invention may be prepared by pressing a mixture of abrasive particles and a minimal amount of a foam binder together into a mold and subsequently allowing the mixture to foam, break down, and harden. Alternatively, high loading densities of abrasive with larger amounts of foam binder may be employed that retain their foam integrity. The resulting abrasive articles are long lasting and may be made low in cost.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation-in-Part of prior application Ser. No. 11/929,963filed on Oct. 30, 2007 which is a Continuation-in-Part of Ser. No.11/846,073 filed on Aug. 28, 2007 which is a Continuation-in-Part ofSer. No. 11/828,270 filed on Jul. 25, 2007 which is aContinuation-in-Part of Ser. No. 11/503,058 filed Aug. 14, 2006, whichclaimed priority to provisional application No. 60/764,110 filed on Feb.1, 2006 and provisional application No. 60/818,571 filed on Jul. 5,2006. Each of the above listed applications are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to abrasive articles. More particularly thisinvention relates to abrasive articles having wearable abrasivesurfaces. The wearable abrasive surfaces of the present invention arecomprised of rigid closed cell polymeric foam materials having very highloading densities of abrasive materials such as aluminum oxide andsilicon carbide. The density of the polymeric foam may be adjusted foroptimum controlled rates of wear. The wearable abrasive articles of thepresent invention may be used on power sanding tools for automotiveapplications such as straight-line and dual action sanders.

2. Description of the Related Art

There are numerous methods that may be employed to sand surfaces. One ofthe more common methods employs sand paper. Sand paper is a thin sheetmaterial usually made of paper that has an abrasive material securelybonded onto one side. Despite its name, the abrasive is rarely if eversand. Commonly used abrasives such as aluminum oxide and silicon carbideare significantly harder than sand and are therefore more effective.This may be especially true when sanding hard materials such as glass orsteel.

Sand paper may be used by hand. This process is often referred to ashand sanding. The process of hand sanding involves using manual labor torepeatedly slide the sand paper back and forth and/or in a circularmotion over the surface until smooth. Numerous textures of abrasives areavailable. Often sanding starts out with a relatively course grade ofsand paper of about 80 grit followed by finer grades of several hundredgrit to finish the job.

One drawback often associated with sand paper is the tendency ofproducing dust that clogs the sand paper. One way to alleviate thisproblem is by using wet or dry Emery cloth. Wet or dry Emery cloth is anabrasive coated cloth having a wide variety of grades. It is designedfor use with water thereby reducing clogging effects.

Another drawback with using sand paper is the tendency for the abrasiveto become dull and fall off from the sand paper backing surface.

Sanding by hand using sand paper is not always practical owing to theamount of labor required. This is especially true for large jobs thatmay take a long time resulting in fatigue.

In order to alleviate the worker fatigue issue in hand sandingoperations, numerous power sanding techniques and/or equipment have beendeveloped. Drum sanding, belt sanding, disc sanding, and orbital sandingare commonplace. These standard power sanding tools often employ someform of sand paper and therefore often suffer from many of thepreviously mentioned drawbacks. In particular is the need to change thesanding surface at regular intervals.

Numerous modifications to ordinary sand paper have been made in order toimprove the overall process. For example, sand paper having a loweredsurface density of abrasive particles is available. This particular sandpaper is made by 3M Corporation of ST. Paul Minn. and is designed foruse in sanding relatively soft materials that quickly gum up ordinarysand paper. Significant improvements in sand paper life may be realizedby reducing the tendency of particulate matter to clog the needed spacesbetween adjacent abrasive particles.

Another improvement that may be made to ordinary sand paper involves theuse of flexible and conformable foam backing. Such backing materialsallow the sand paper to conform to surface contours thereby more rapidlysmoothing contoured surfaces. Individual pieces of sand paper may beapplied to foam pads or conversely, foam pads having previously attachedsand paper may be employed. For example, Finishing Buddies (Mona LisaProducts 10770 Moss Ridge Road Houston, Tex., 77043) is a completesanding tool kit consisting of a steel wool pad, oval sanding disc, andcoarse, medium, and fine sanding pads. The oval pad is relatively rigid,and the three other sanding pads have a softer foam backing that has agreater degree of flexibility. This sanding kit is designed for slowhand sanding and finishing operations.

There are numerous flexible sanding surfaces, components, and articlescomprised of abrasive materials fixedly attached to flexible foambackings. Of particular interest is a sanding system employing arelatively thin rigid foam backing disclosed in U.S. Pat. No. 6,923,840and assigned to 3M Innovative Properties Company, St. Paul Minn. (US).U.S. Pat. No. 6,923,840 discloses a flexible abrasive product comprisedof an open cell foam backing, a foraminous barrier coating, and a shapedforaminous abrasive coating. The top abrasive coating is discontinuousand allows for holding lubricants such as water as well as spaces forremoval of debris.

U.S. Pat. No. 6,949,128 also assigned to 3M, discloses a method formaking a foam backed abrasive article having embossed raised areas.

U.S. Pat. No. 3,401,490 discloses a method for forming an abrasivearticle having a resiliently yielding open cell meltable base which ispassed under a heated roll to melt the surface to a desired depthfollowed by application of abrasive particles to the melted surface. Theresult is a flexible foam based abrasive article capable of followingirregular, uneven, or sunken surfaces.

U.S. Pat. No. 6,997,794 by James Matthew Pontieri discloses a disposablesanding device fabricated as a continuous rope like article adapted forselective segmentation. This device may employ a foam central portionalong with an abrasive outer portion. In particular the flexiblecylindrical geometry illustrated in several embodiments of the inventionlends itself to the hand sanding of difficult to reach contours and mayprove especially useful in woodworking applications.

There are numerous flexible foam based cleansing and scouring padshaving added abrasive materials. An example of this can be found in U.S.Pat. No. 3,377,151. U.S. Pat. No. 3,377,151 discloses a method formaking flexible resilient cleansing and scouring pads having an abrasivesurface. A thermoplastic foam web material is hot laminated to abrasiveweb material. In addition, one or more cleansing materials may be added.

U.S. Pat. No. 3,619,843 discloses sponges having dry impregnatedmaterials. In this invention, impregnated sponges are prepared by aprocess that deposits particulate material on one surface of the spongeand subsequently pierces the sponge with spikes to form crevicesfollowed by drawing particulate material into the crevices. The resultis a modified sponge suitable for surgical and sanitizing applications.

Also of interest are flexible open cell foam scouring and cleaning padshaving numerous protrusions. These pads are disclosed in U.S. Pat. No.4,055,029 by Heinz Kalbow, Lichgasse. The flexible pad has numerousprotrusions on the working surface having an abrasive layer. U.S. Pat.No. 4,111,666 also by Heinz Kalbow discloses a method of manufacturingflexible abrasive cleaning pads along with improvements in tearresistance.

U.S. Pat. No. 4,421,526 discloses polyurethane foam cleaning padscomposed of a densified flexible sponge like polyurethane foam materialimpregnated with various cleansing additives. Excessive mixing of thefreshly blended polymers inhibits foam formation long enough to add thecleansing ingredients. The resulting pads have added strength due tocollapsed, ruptured, and distorted cells along with fibers that resultfrom the specific mixing process employed. The result is an unusuallystrong dense flexible cleaning pad capable of absorbing substantialamounts of water that releases additives along with absorbed water ongentle squeezing.

U.S. Pat. No. 4,594,362 discloses a dry type textile cleaning articlecomprised of a friable hydrophilic polyurethane foam with incorporatedabrasive particles as well as other additives. The abrasive particlesare chemically bonded to the foam using silane coupling agents therebyreducing their tendency to separate from the mass and subsequentlydamage cloth material.

Wet sanding abrasive foam compositions are disclosed in U.S. patentapplication # 20080020678 titled “Discontinuous Abrasive ParticleReleasing Surfaces” having serial # 828270. In this invention, watersoftening properties are imparted to an abrasive loaded foam surface toprevent deep scratches from coarse abrasive particles, and to aid inabrasive paste formation. Attempting to use these wet abrasivecompositions in dry sanding operations results in an abrasive surfacethat dulls, clogs up and may not have the proper controlled rate ofwear.

While the above described examples of foam based abrasive articlesprovide a wide variety of uses, there exists a need in the art forsemi-rigid or rigid abrasive articles having a wearable surface thatrenews itself during use that may be employed in hand and/or low speeddry abrasive operations including dry sanding, and/or dry grindingoperations.

Many of the above described examples outline the use of foam withabrasive materials in order to achieve certain advantageous anddesirable properties. Still others outline some of the more simplemethods and materials commonly employed in dry sanding, and grinding.While generally effective for dry sanding, and grinding, there exists aneed in the industry for further improvements in dry abrasiveoperations.

For example, improvements in dry abrasive operations may be realized inthe area of dual action sanding tools. Dual action sanding tools employthe action of simultaneous spinning and vibration. This dual actionresults in rapid and relatively uniform sanding. Dual action sandingtools may be used with the dry sanding compositions outlined in thepresent invention to provide continuous non-clogging use. Additionally,The action of straight-line sanding tools tends to reduce cloggingeffects when sanding surfaces with the dry sanding compositions outlinedin the present invention as well.

Despite numerous advancements in the field of abrasives there is a needfor abrasive articles having a wearable surface that renews itselfduring use that may be employed in dry abrasive operations.

It is an object of this invention to provide abrasive surfaces for dryhand sanding applications.

It is a further object of this invention to provide numerous grades ofabrasive surfaces for low dry hand sanding applications.

It is a further object of this invention to provide abrasive surfacesdry sanding applications employing dual action and straight-line sandingtools resistant to excess build up of debris.

It is a further object of this invention to provide abrasive surfacesfor both hand and power dry sanding applications having a controlledlevel of rigidity.

It is a further object of this invention to provide abrasive surfacesfor both hand and power dry sanding applications that are low in cost.

It is a further object of this invention to provide simple methods forproducing abrasive surfaces for hand and power dry sanding applications.

It is a further object of this invention to provide abrasive surfacesfor hand and power dry sanding applications that may be used forextended periods of time without wearing out.

Finally, it is an object of this invention to provide abrasive surfacesfor hand and power dry sanding applications that have wear rates thatresult in continuous renewal of working surfaces during use.

SUMMARY OF THE INVENTION

This invention proposes articles for dry sanding applications employingwearable abrasive surfaces that renew themselves on continued use. Thedry sanding articles of the present invention have wearable abrasivesurfaces comprised of closed cell rigid polymeric foam loaded with largeamounts of abrasive particles. Dense wearable abrasive surfaces may beformed by compressing a mixture of abrasive particles with a minimalamount of liquid polyurethane foam resin together. Compression of theabove described wearable abrasive surfaces may be take place in a moldthereby forming them into specific shapes. Wearable abrasive surfaces ofa lower density may be formed by mixing substantial amounts of abrasiveparticles together with liquid polyurethane foam resins having a densityof 8 or more pounds per cubic foot.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the advantagesthereof will be readily obtained as the same becomes better understoodby reference to the detailed description when considered in connectionwith the accompanying drawings, wherein:

FIG. 1 shows an abrasive surface suitable for Velcro attachment to astraight-line sander.

FIG. 2 shows a cross sectional view of a dense abrasive composition ofthe present invention.

FIG. 3 shows an abrasive article suitable for Velcro attachment to adual action sander.

FIG. 4 shows a cross sectional view of a foam based abrasive surfacesuitable dry sanding applications.

FIG. 5 shows a cross sectional view of a sanding disk having Velcroattachment means for a rotary or dual action tool.

FIG. 6 shows a hand held abrasive article suitable for dry hand sandingapplications comprised of a handle portion fixedly attached to wearableabrasive surface.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an abrasive surface suitable for Velcro attachment to astraight-line sander. Abrasive straight line sanding pad 2 is shownhaving top abrasive pad portion 4 attached to soft Velcro attachmentportion 6. Also shown is top exposed major sanding surface portion 8.Straight line sanding pad 2 attaches to a straight line sanding toolwith Velcro attachment portion 6.

FIG. 2 shows a cross sectional view of a dense abrasive composition ofthe present invention. Dense abrasive composition 10 is shown havinghard abrasive particles 12 along with spaces 14 between hard abrasiveparticles 12. Spaces 14 between hard abrasive particles 12 provideseparation between hard abrasive particles 12. This separation allowsfor exposure of individual hard abrasive particles 12 while at the sametime providing space for debris generated during the sanding process.

The dense abrasive composition of FIG. 2 forms when there is not enoughliquid polymeric foam resin in the mix to properly foam. Dense abrasivecompositions form at an abrasive loading density of about 90% by weightof the mix. This value is dependent on the polymeric resin system, theabrasive material, and the abrasive particle size. Dense abrasivecompositions of the present invention may used to produce working toolshaving a controlled rate of wear. Abrasive compositions of this naturemay be made to work for hand sanding as well as power sandingapplications. Abrasive compositions employing 92% by weight of siliconcarbide abrasive to 8% by weight of liquid polymeric foam resin exhibitdesirable sanding properties having surfaces that renew themselves at agood rate and are resistant to clogging effects from prolonged use. Thefollowing examples will now be given in detail.

EXAMPLE 1

8 grams of polyurethane resin A SP-328-8 from Silpak (Silpak INC 470East Bonita AVE Pomona, Calif. 91767 Tel # (909) 625-0056) were placedinto a 1 liter polyethylene wide mouthed container. To this were added 8grams of polyurethane resin B SP-328-8 from Silpak. These two resinswere then blended together and mixed thoroughly. 184 grams of 120 gritsilicon carbide abrasive were then added and mixed thoroughly with anelectric mixer to form a damp powder. This damp powder was then placedinto a 2½″×4½″×1″ deep cavity of a silicone mold. This mixture was thencompressed with a wooden block by applying about 40 pounds of pressurefor a period of one minute. The wooden block was then removed and themixture allowed to cure for 20 minutes. The partially cured part wasthen removed from the mold. The bottom surface was then sanded down toopen expose an abrasive surface. The part was then allowed to stand for24 hours to thoroughly cure. This part was then attached to a plastichandle with polyurethane adhesive. Once cured, the tool was used to sandautomotive paint and primer from a metal surface. Sanding was rapid. Thesanding surface released abrasive particles at a rate sufficient torenew the surface without dulling. The working surface of the tool hadlittle tendency toward plugging up. This tool behaved in a similarmanner to 320 grit sandpaper. Furthermore, despite the fact that 120grit abrasive was used to make the tool, deep scratches were notobserved.

EXAMPLE 2

The above experiment was repeated using 46 grit silicon carbideabrasive. Results were substantially the same with the sanding surfaceof the tool behaving like 100 grit sandpaper.

Samples of both abrasive materials outlined above were broken off fromthe tools. Microscopic examination revealed about 50% void space with noevidence of closed cells. No foam structure was present. The abrasiveparticles were spaced uniformly throughout the mix forming an aggressiveabrasive composition. This clearly shows that the 92% abrasive loadingdensity in the mix was sufficient to disrupt the formation of foam.Disruption of the foam may be said to have occurred when bubblesnormally present in the foam are no longer discernable under microscopicexamination.

FIG. 3 shows an abrasive article suitable for Velcro attachment to adual action sander. Abrasive dual action sanding pad 18 is shown havingtop abrasive pad portion 20 attached to soft Velcro attachment portion22. Also shown is top exposed major sanding surface portion 24. Dualaction sanding pad 18 attaches to a Dual action sanding tool with Velcroattachment portion 22. Dual action sanding pads attach to dual actionsanding tools. Dual action sanding tools combine the simultaneousactions of both spinning and vibration. These two combined actions helpto remove debris from the sanding area thereby reducing clogging effectsthat may occur at exposed major sanding surface portion 24 during use.

FIG. 4 shows a cross sectional view of a foam based abrasive surfacesuitable dry sanding applications.

Abrasive material 26 is shown in cross sectional view. Abrasive material26 is shown having abrasive particles 28 embedded within high densityfoam matrix material 30. Abrasive particles 26 may comprise a materialselected from the group consisting of aluminum oxide, silicon carbide,zirconia, diamond, ceria, cubic boron nitride, garnet, ground glass,quartz, and combinations thereof. Also shown are voids 32. Voids 32result from the foaming action of the polymeric foam based resinmaterials employed.

Foam based dry sanding compositions may be prepared by blendingsubstantial amounts of silicon carbide abrasive with liquid polyurethanefoam resins having a density of 8 or more pounds per cubic foot. Thesehigher density foam compositions may be loaded with larger amounts ofabrasive without falling apart. This may require the use of lowviscosity resin materials or alternatively may be prepared by thinningdown higher viscosity resin materials with a non-reactive solvent.Additionally, solvents having some reactivity toward the isocyanateportion of the mix may be added to modify the foaming characteristics ofthe mix. Non-reactive solvents include solvents having enough polaritydo be compatible with both the polyol and isocyanate resins but lackingreactive functional groups. Generally speaking, hydroxyl groups arereactive toward isocyanate resins. Alcohols and ketones having enolalcohols (enol keto tautomerization) may react with isocyanate resinsand should be considered reactive with the system.

Additionally, the resin ratio of polyol resin to isocyanate resin shouldbe close to stoicheometric. One practice used in the industry is to usea very slight excess of isocyanate resin in the mix of about one percentby weight. Although both flex agents as well as stiffening agents may beadded to modify resin properties, working abrasive compositions havebeen made that work in straight-line sanding tools without theseadditives. Additionally, Working compositions have been prepared fordual action sanding tools by limiting the thickness of the abrasivesurface to 0.2″. This limited thickness allows for some tool flexibilitywithout the need to use flex agents. Abrasive loading density and foamdensity may then be used to provide a suitable tool life without theneed to increase the thickness of the abrasive surface.

The density of polyurethane foam materials may be increased by blendingnon-foaming polyurethane resins with foaming polyurethane resins. Incertain circumstances it may be desirable to blend foaming polyurethaneresins with non-foaming polyurethane resins in order to increase foamdensity, modify surface hardness, and control bubble size anduniformity. This blending is easily carried out by thoroughly mixing theresins prior to adding the abrasive.

The abrasive loading density needed for these tools requires about 270grams of silicon carbide abrasive for each 100 grams of resin mix. Belowthis value, sanding is slow and surface clogging may occur. This ratioof abrasive to resin mix results in structural integrity. A foam may beconsidered to have structural integrity if bubbles in the foam remainintact once cured.

The abrasives themselves may have various particle shapes. Siliconcarbide abrasives tend to be somewhat planar. Because of this, there isa tendency of silicon carbide abrasive particles to align themselves inthe direction of foam growth during manufacture. Sanding surfaces cut atright angles to foam growth may therefore exhibit better sandingproperties that sanding surfaces cut along the direction of foam growth.Additionally, it may be desirable to blend different abrasive materialshaving the same grit value together to provide sanding surfaces havingimproved properties.

FIG. 5 shows a cross sectional view of a sanding disk having Velcroattachment means for a rotary or dual action tool. Abrasive dual actionsanding pad 34 is shown having top abrasive pad portion 36 attached tosoft Velcro attachment portion 38. Also shown is top exposed majorsanding surface portion, on the opposite side of the Velcro attachment38. Dual action sanding pad 34 attaches to a Dual action sanding toolwith Velcro attachment portion 38. Dual action sanding pads attach todual action sanding tools. Dual action sanding tools combine thesimultaneous actions of both spinning and vibration. These two combinedactions help to remove debris from the sanding area thereby reducingclogging effects that may occur at exposed major sanding surface portionduring use. Exposed abrasive particles 42 are shown protruding frommajor sanding surface.

FIG. 6 shows a hand held abrasive article suitable for dry hand sandingapplications comprised of a handle portion fixedly attached to wearableabrasive surface.

FIG. 6 shows a hand held abrasive article that may be used to dry sandautomotive surfaces. Hand held abrasive article 44 is shown comprising amain handle portion 46 and a major abrasive surface working portion 48.Also shown is side groove 50. Side groove 50 provides an ergonomic fitto the hand for easier use. Hand held abrasive article 44 is shownhaving major abrasive surface portion 48 fixedly attached to main handleportion 46. Major abrasive surface portion 48 may be comprised of theabrasive dry sanding composition of FIG. 4.

Those skilled in the art will understand that the preceding exemplaryembodiments of the present invention provide foundation for numerousalternatives and modifications. These other modifications are alsowithin the scope of the limiting technology of the present invention.Accordingly, the present invention is not limited to that preciselyshown and described herein but only to that outlined in the appendedclaims.

1. A composition of matter for dry sanding applications comprising: (a)from about 1 part by weight of polymeric foam with a density of at least8 pounds per cubic foot; and (b) from about 2.7 to about 8 parts byweight of abrasive particles, whereby said composition of matter hasstructural integrity.
 2. The composition of matter of claim 1 whereinsaid polymeric foam is polyurethane.
 3. A composition of matter for drysanding applications comprising: (a) about 1 part by weight of polymericfoam; and (b) at least 8 parts by weight of particles, whereby loadingdensity of said particles causes disruption of said foam.
 4. Thecomposition of matter of claim 3 wherein said particles is comprised ofabrasive particles.
 5. The composition of matter of claim 3 furthercomprising of void spaces between said particles of less than about 70%by volume.
 6. The composition of matter of claim 3 wherein saidpolymeric foam is polyurethane.
 7. An abrasive article for dry sandingapplications comprised of a dense abrasive composition.
 8. The abrasivearticle of claim 7 further comprising a Velcro attachment.
 9. Theabrasive article of claim 8 wherein said Velcro attachment is used toattach said abrasive article to a dual action sander.
 10. The abrasivearticle of claim 8 wherein said Velcro attachment is used to attach saidabrasive article to a hand sander.
 11. The abrasive article of claim 8wherein said Velcro attachment is used to attach said abrasive articleto a straight line sander.